Phase precipitation and time–temperature-transformation diagram of Hastelloy X

Transmission electron microscopy (TEM) was employed to study the phase precipitation in Hastelloy X heat-treated at 750, 850, and 900°C for 26 and 100 h. Phase identification was made by electron micro-diffraction and energy dispersion spectroscopy (EDS) X-ray micro-chemical analysis. In addition to the fcc matrix, four different precipitation phases were observed: M6C, M23C6, σ, and μ. The current observations were combined with literature results to build a time–temperature-transformation (TTT) diagram for this alloy. This TTT diagram depicted time–temperature regimes where various phases were formed; thus, it provided information about the general precipitation kinetics for the alloy.